The present invention generally relates to an implantable device and method for producing same and, more particularly, to an implantable device that has a low impedance carbon coating over a porous substrate. The carbon coating has a lattice structure that is formed onto a porous substrate of an implantable device by a process that includes the plasma deposition of carbon in an energized gaseous environment within which a hydrocarbon is degraded and its carbon is deposited onto the porous substrate.
It has been recognized that in many medical applications, it is desirable to provide a tissue-compatible porous surface. The porous nature of such a surface allows tissue to grow into the porous surface in order to more effectively incorporate the device into the body. Such ingrowth assists in holding the device in place within the body.
Porous platinum surfaces are especially desirable in this regard because of their superior electrical properties; however, because porous platinum coatings tend to be unusually expensive, high-technology alloys have been utilized instead of platinum, and quite successfully, as porous coatings. It would be desirable to provide a relatively inexpensive porous surface that exhibits superior electrical properties and that is of especially enhanced stability and uniformity. Considerations important to stability include resistance to current reversals that might be encountered during use.
Particularly advantageous would be a stable and uniform surface that also maintains an advantageously low polarization impedance. In general, the location of greatest impedance that is experienced with these types of devices is at the interface between the tissue and the outer surface of the device, and attempts and proposals have been made to modify the outer surface of these types of devices in order to improve characteristics of the overall device. Because materials such as carbon have an extremely low electrical impedance, prior activities in this regard include attempts and proposals for using carbon at the interface between such devices and the living tissue into which they are implanted.
Included in such activities have been the utilization of a porous carbon layer over a surface of a shaped, implantable device, appliance or implement. Typically, these porous carbon layers are laid down by sintering or other procedures that include subjecting the surfaces to high temperatures, which often result in a pyrolytic carbon coating that is vitreous or glassy and somewhat amorphous. Additionally, when carbon is laid down by a procedure such as sintering, the carbon is coated in bulk quantities first, and then the bulk carbon layer is sintered or otherwise modified on a scale which is that of a formed coating of substantial thickness. This tends to require very harsh treatment conditions that can result in a final product which is of reduced stability and uniformity.
There is accordingly a need for implantable devices having carbon surfaces that are porous to promote tissue ingrowth thereinto while avoiding harsh treatment of bulk-scale carbon coatings. Also to be avoided is the vitreous condition that high temperature treatments impart to a carbon coating. It is further desirable to simultaneously provide a carbon coating that is unusually uniform in its thickness and pore network even when coated onto uneven surfaces in order to provide a carbon coating that is both thin and uniformly structured, and which will provide minimal impedance and adequate strength under current-transmitting conditions.
Such needs and objectives are accomplished by the present invention by forming a porous carbon coating onto a porous substrate or surface of an implantable device in accordance with a procedure that incorporates plasma deposition and degradation to provide a porous carbon coating that is formed on a generally molecular level in order to impart a porous carbon lattice structure over the porous substrate. The porous carbon plasma deposition procedure includes subjecting the substrate surface to a gaseous environment including a hydrocarbon and energizing that gaseous environment in order to degrade the hydrocarbon, typically in association with polymerization of the hydrocarbon, to form the porous carbon lattice structure.
Accordingly, an object of the present invention is to provide improvements in implantable devices.
Another object of the present invention is to provide an implantable device and process for producing same, which device is suitable for implantation within a living body and for the reception of tissue ingrowth into a carbon coating that is structured by a porous substrate thereunder.
Another object of the present invention is to provide an improved device and process which utilizes plasma polymerization techniques for the formation of a thin carbon coating of low polarization impedance and exceptional stability.
Another object of the present invention is to provide an improved device and process wherein plasma polymerization techniques are tailored in order to deposit a carbon coating on a porous shaped substrate.
Another object of this invention is to provide an improved process and product produced thereby which includes coating a carbon layer under generally flowing conditions whereby a carbon lattice is laid down onto a shaped substrate in a uniform condition that closely conforms to the shape of the substrate, including convoluted surfaces thereof.
Another object of the present invention is an improved method and implantable device that incorporates a carbon coating that is deposited at relatively low temperatures.
Another object of this invention is to provide an improved implantable device that can be used as either an anode or a cathode and that is inert in implantable environments.
Another object of the present invention is an improved process and product produced thereby which provides a porous carbon coating over a variety of porous substrates.
These and other objects, features and advantages of the present invention will be clearly understood through a consideration of the following detailed description.